Well, after blowing all that hot air - I fixed it. I simply opened a new configuration and started from the basics. I just kept plugging away at different settings until it worked perfectly. I inserted an ASIO send/return...uh....insert into the channel strip.

Anyway - yes, the crosstalk is very low - especially considering that input was open! Now, it's effectively muted so any noise is buried in the noise floor. My operational distortion numbers are now in the 0.005% range, which is perfectly fine for me. My goal was to improve my old system by an order of magnitude and I feel it was successful.

Pete's little test box is a smashing success, in my opinion. I "upgraded" some of the components as outlined in this thread. It likely made little difference, but having a skid of 0.1% resistors in my lab doesn't hurt things.

I'm using the same box, but I soldered sheets of copper tape inside as well as grounded the selector knob shaft and each pushbutton switch case. I don't see ANY 60Hz residuals in my FFT.

EDIT: I believe I was using Hanning window for that screenshot, but it's a trivial affair now. It seems that there was a divergent signal path being fed back. The software itself is rather buggy, too - especially on ASIO drivers. In my case, I found a solution and - at least for now - don't intend to putz with it.

I'm using the licensed Audiotester.de and the E-Mu 1212m (with Windows 7 drivers) in a machine running Windows 7 Home Premium. The computer is stripped down to the basics so as not to interfere with the measurement system.

1. The interface I built has a big gap in its attenuation settings. I was trying to test a 100W amplifier - which is ~30V. This is above the 20V setting, so I chose the nest higher...200V. The problem is that the attenuation is so great that the 1212m doesn't tell AudioTester that the signal is large enough. No amount of gain on the 1212m interface gets me adequate input levels.
2. I am forced to calibrate the sound card without the Interface. An external input signal (~15V peak) is never high enough with the interface to calibrate AudioTester's max reading...
3. The RMS meter, though calibrated against an HP 3400A, isn't accurate in the 200V range. I measured 29V RMS on my oscilloscope while the Interface read 21V. Of course, being 21V, I couldn't check accuracy on the 20V scale.
4. Power/THD tests through AudioTester just clip the interface badly. Because the level is too low on the 200V range, I have to perform the test at 20V - a classic catch-22.

So...should I modify it for a 30 and 100V range? Or, should I change the sound card to something else? Any ideas?

I'm using the licensed Audiotester.de and the E-Mu 1212m (with Windows 7 drivers) in a machine running Windows 7 Home Premium. The computer is stripped down to the basics so as not to interfere with the measurement system.

1. The interface I built has a big gap in its attenuation settings. I was trying to test a 100W amplifier - which is ~30V. This is above the 20V setting, so I chose the nest higher...200V. The problem is that the attenuation is so great that the 1212m doesn't tell AudioTester that the signal is large enough. No amount of gain on the 1212m interface gets me adequate input levels.
2. I am forced to calibrate the sound card without the Interface. An external input signal (~15V peak) is never high enough with the interface to calibrate AudioTester's max reading...
3. The RMS meter, though calibrated against an HP 3400A, isn't accurate in the 200V range. I measured 29V RMS on my oscilloscope while the Interface read 21V. Of course, being 21V, I couldn't check accuracy on the 20V scale.
4. Power/THD tests through AudioTester just clip the interface badly. Because the level is too low on the 200V range, I have to perform the test at 20V - a classic catch-22.

So...should I modify it for a 30 and 100V range? Or, should I change the sound card to something else? Any ideas?

Thanks.

Have you run the amp at less than full output, say 18Vrms using the 20v scale? I use the sound card GUI volume control to set the card output voltage. I've been testing my amp using the 20v scale, but, it also works with the 200v scale, just jumps up the noise floor by about 10db (attenuation resistor noise?).

Have you run the amp at less than full output, say 18Vrms using the 20v scale? I use the sound card GUI volume control to set the card output voltage. I've been testing my amp using the 20v scale, but, it also works with the 200v scale, just jumps up the noise floor by about 10db (attenuation resistor noise?).

I use the juli@ card and AudioTester.

Ken

Yes, but I want to measure THD/Power. It's fine until the amplifier is driven to high output, but the interface is clipping long before that.

The 200V scale attenuates the signal so much that the Patchmix (1212m GUI) can't give me enough gain to register in AudioTester. Like I said, Catch-22.

Yes, but I want to measure THD/Power. It's fine until the amplifier is driven to high output, but the interface is clipping long before that.

The 200V scale attenuates the signal so much that the Patchmix (1212m GUI) can't give me enough gain to register in AudioTester. Like I said, Catch-22.

1212M FOR SALE. Make me an offer!!

I don't know if it's your sound card. As I said, I haven't had the issue of the of switching between different levels of 2, 20 and 200v scales. In all cases, the signal shows up in AudioTester. I would look at the sound card interface (PMillet device) to make sure that there isn't something wrong with the the 200v circuit, wrong resistor values, cold solder joint ect. Put a signal into it and a voltage meter on the output, you should see signal. I forget what resistor values he used, but, they are there on the schematic, figure out the attenuation and see if the applied signal is adjusted accordingly.

As an aside, I have never gotten the THD/Power plot to work. More of a AudioTester problem and obtuse instructions. Can't figure out what value to set in the AudioTester parameters to get a full plot. If you get the THD/power to work, maybe you can post instructions.

I don't know if it's your sound card. As I said, I haven't had the issue of the of switching between different levels of 2, 20 and 200v scales. In all cases, the signal shows up in AudioTester. I would look at the sound card interface (PMillet device) to make sure that there isn't something wrong with the the 200v circuit, wrong resistor values, cold solder joint ect. Put a signal into it and a voltage meter on the output, you should see signal. I forget what resistor values he used, but, they are there on the schematic, figure out the attenuation and see if the applied signal is adjusted accordingly.

As an aside, I have never gotten the THD/Power plot to work. More of a AudioTester problem and obtuse instructions. Can't figure out what value to set in the AudioTester parameters to get a full plot. If you get the THD/power to work, maybe you can post instructions.

Ken

The Interface is 100%.

I didn't mean to imply that the 200V scale doesn't work - it just attenuates the signal more than I can compensate with PatchMix to get AudioTester to see the initial signal in THD/Power (if it worked). I can start in the 20V scale and click over to 200V, but I'd rather not.

I was wondering about the veracity of the Power/THD mode. AudioTester screens make no sense in the THD/Power tests. The Y axis is labeled %, but the digits are -140 to 0 while the X axis in mV That makes no sense. I guess I'll have to buy another test suite. Any suggestions?

That's why you see, 1, 2, 5, 10 on oscilloscopes and other measuring apparatus. Less seen is 1, 3, 10.

You can easily add a pot to the signal that is a bit too high. But, would you need a balanced pot to allow the card to output and input balanced signals? You are using balanced throughout the test arrangement?